KR102013334B1 - Ion implanter and method of operating the same - Google Patents

Abstract

The ion implanter includes a platen having a clamping surface configured to support a wafer for processing with ions, the platen also providing an AC signal to at least one pair of electrodes, at least one pair of electrodes below the clamping surface and And a clamping power supply configured to provide a sensed signal representative of the AC signal, and a controller. The controller is configured to receive a sensed signal from the clamping power supply when there is no clamped wafer on the clamping surface. The controller is further configured to monitor the sensed signal and determine whether the sensed signal represents deposits on the clamping surface that exceed a predetermined deposit threshold.

Description

ION IMPLANTER AND METHOD OF OPERATING THE SAME}

Cross Reference of Related Applications

This application claims the benefit of US Provisional Patent Application 61 / 614,564, filed March 23, 2012, which is incorporated herein by reference.

Field of technology

The present invention relates to platens and, more particularly, to platen clamping surface monitoring.

Ion implantation is a standard technique for introducing conductivity-modifying impurities into semiconductor wafers. Ion implantation may be performed by a beamline ion implanter or a plasma doped implanter. In a beamline ion implanter, dopant gas may be ionized at the ion source and ions may be extracted from the ion source and accelerated to form a beam of desired energy. The ion beam can then be directed to the front surface of the wafer supported by the platen. The wafer may be a semiconductor substrate, and active ions within the ion beam may be embedded within the crystal lattice of the semiconductor wafer to form the desired conductive region after subsequent annealing steps. The plasma doped injector places the wafer supported by the platen in the plasma chamber. Plasma may be generated in the plasma chamber, and ions from the plasma are accelerated towards the wafer, for example by biasing the wafer and / or the plasma chamber.

Most platens are electrostatic chucks that use electrostatic forces to clamp the wafer to the clamping surface of the platen. The clamping surface of the platen is on the clamping surface due to deposits of ion beam byproducts, for example when the ion beam collides with dose Faraday cups for extended periods of time in one example. Due to the accumulation of arsenic deposition, it can become dirty over time.

Deposits on the clamping surface of the platen are particularly problematic in hot ion implants or hot implants. Integrated circuit manufacturers are experimenting with hot implants for their next generation device development, eg, pin field effect transistors (FinFETs). Hot injections typically occur at temperatures higher than 150 ° C. Some hot injections occur at temperatures higher than 300 ° C., while other hot injections occur between 300 ° C. and 750 ° C. In addition to typical deposits from ion beam byproducts, some deposits are attracted more to the hot clamping surface. In addition, thermally activated reactions can occur on the hot clamping surface of the platen to produce additional deposits during the hot implantation processes. Trace amounts of materials such as carbon, fluorine, tungsten, and hydrogen may be present in the ion implanter. These materials may contribute to thermally activated reactions to create additional unwanted deposits on the clamping surface of the platen. One example of this is the decomposition of refractory metals from gas precursors. Another example is the decomposition of carbon from the reactants of methane.

Accumulation of deposits on the clamping surface of the platen negatively affects the clamping force provided by the platen. The deposits may shunt electrostatic fields holding the wafer. If not cleaned, accumulation of deposits can reach transient levels that cause unintended wafer drop and wafer breakage. A sputter clean process in which low energy ions are directed to the clamping surface of the platen can be used to efficiently clean the clamping surface. However, because the amount and location of deposits on the clamping surface depend on a number of variables, it is difficult to predict when a sputter clean process is needed. This can lead to excessive interruptions of ion processing for sputter cleaning. This can reduce throughput performance or the number of wafers that can be processed over a given time period, thus negatively impacting the total cost of production. Otherwise, there is a risk of wafer drop and destruction if not cleaned at a sufficient frequency. In addition, it is difficult to monitor the amount of deposits in the field where the ion implanter processes wafers.

Thus, there is a need in the art for platen surface monitoring for the indication of excessive deposit accumulation.

According to one aspect of the invention, an ion implanter is provided. The ion implanter includes a platen having a clamping surface configured to support a wafer for processing with ions, the platen also providing at least one pair of electrodes below the clamping surface, an AC signal to the at least one pair of electrodes. And a clamping power supply configured to provide a sensed signal representative of the AC signal, and a controller. The controller is configured to receive a sensed signal from the clamping power supply when there is no clamped wafer on the clamping surface. The controller is further configured to monitor the sensed signal and determine whether the sensed signal represents deposits on the clamping surface that exceed a predetermined deposit threshold.

According to another aspect of the invention, a method of operating an ion implanter comprises: providing an AC signal to at least a pair of electrodes of a platen having a clamping surface; Monitoring the sensed signal indicative of an AC signal when there is no clamped wafer on the clamping surface; And determining whether the sensed signal indicates deposits on the clamping surface that exceed a predetermined deposit threshold when there is no clamped wafer on the clamping surface.

For a better understanding of the invention, reference is made to the accompanying drawings, which are incorporated herein by reference.
1 is a schematic diagram of an ion implanter in accordance with one embodiment.
2A is an enlarged partial cross-sectional view of a clean clamping surface of a waferless platen.
FIG. 2B is an enlarged partial cross sectional view of the clean clamping surface of the platen of FIG. 2A with the wafer present; FIG.
FIG. 2C is an enlarged fragmentary cross-sectional view of the dirty clamping surface of the platen of FIG. 2A without the wafer. FIG.
3 is a plot of time versus current of an AC signal provided by the clamping power supply of FIG. 1.
4 is a cross-sectional view of portions of the ion implanter of FIG. 1 oriented at an angle of incidence for a sputter clean process.

Referring to FIG. 1, a block diagram of an ion implanter 100 is illustrated. Ion implanter 100 includes an ion source 102, an end station 105, and a controller 120. The end station 105 may include a platen 112, a clamping power supply 172, a robot 132, a tilt mechanism 118, and a heater 106. . Ion source 102 is configured to produce ion beam 104. The ion implanter 100 is another beamline component known to those skilled in the art for manipulating the ion beam 104 when the ion beam is directed towards the front surface of the wafer 110 supported by the platen 112. May be included between the ion source 102 and the platen 112. For ease of illustration, the wafer 110 is shown phantom slightly away from the clamping surface 114 of the platen 112. Those skilled in the art will appreciate that during operation, wafer 110 is in intimate contact with clamping surface 114. Wafer 110 may be a semiconductor wafer having a disk shape having a diameter of 300 millimeters (mm) or other diameter sizes. The clamping surface 114 of the platen 112 may have a similar disk shape to support the wafer 110.

Ion beam 104 may be a ribbon beam or a spot beam as is known in the art. Ion beam 104 may be distributed across the entire front surface of wafer 110 by ion beam movement, wafer movement, or a combination of both. In one embodiment, ion beam 104 may be a ribbon beam having a substantially rectangular cross-sectional shape. The long dimension of the ribbon beam may be at least three times larger than the short dimension. The wafer may be mechanically moved in a direction perpendicular to the long dimension of the ribbon beam to distribute the ribbon beam over the entire front surface of the wafer 110.

End station 105 includes platen 112. Platen 112 is an electrostatic chuck with top dielectric layer 168 forming clamping surface 114. The platen 112 also has at least a pair of electrodes 160, 162 below the clamping surface 114. In some embodiments, the platen includes three pairs of electrodes or a total of six electrodes. The clamping power supply 172 is configured to provide an alternating current (AC) signal to the electrodes 160, 162 to generate electrostatic forces for securing the wafer 110 to the clamping surface 114 of the platen 112. do. The AC signal is the current that changes direction in the cycles. Examples of AC signals include square wave signals, sinusoidal signals, or pseudo-square wave signals. Preferably, the clamping power supply 172 also includes circuitry 171 configured to provide a sensed signal indicative of an AC signal.

End station 105 may also include automated wafer processing equipment for introducing wafers to and removing wafers from platen 112. The automated wafer processing equipment can include a robot 132 that enables movement of wafers to and from the platen 112. The automated wafer processing equipment also enables the movement of wafers from atmospheric conditions to the platen 112 via load lock and out of the load lock after ion treatment back to atmospheric conditions. It may include additional robots needed for the purpose.

Tilt mechanism 118 is configured to tilt platen 112 with respect to ion beam 104. In one embodiment, the tilt mechanism 118 can tilt the platen 112 about two orthogonal axes. Rotating platens or roplats can have these capabilities.

The end station 105 may also include a heater 106 configured to heat the wafer 110 for hot implant. The heater 106 may be external to the platen 112 and may provide heat directly to the wafer 110 located on the platen when the wafer 110 is positioned adjacent to the heater. For example, the heater 106 may include one or more lamps to provide heat to the wafer for hot implants. Alternatively, the heater 106 may be located within the platen 112, for example as a heating element or heat trace. Regardless of whether the platen 112 is internal or external (or both are used), the heater 106 is configured to enable hot injections at temperatures higher than 150 ° C. The heater 106 is also configured to enable hot implants at wafer temperatures higher than 300 ° C, including between 300 ° C and 750 ° C.

Controller 120 may be or include a general purpose computer or network of general purpose computers that may be programmed to perform desired input / output functions. Controller 120 may also include other electronic circuitry or components, such as application specific integrated circuits, other hardwired or programmable electronic devices, discrete element circuits, and the like. Controller 120 may also include communication devices, data storage devices, and software. The controller 120 can receive signals from various systems and components such as the clamping power supply 172, the robot 132, the tilt mechanism 118, the heater 106, and the ion source 102 and In order to control them, output signals may be provided to each.

In operation, a plurality of wafers may be cycled to and from the platen 112 for processing with the ion beam 104. In the time periods between successive wafers processed with ion beam 104, no wafer is clamped to platen 112. Over time, deposits 150 may accumulate on the clamping surface 114 of the platen 112. In FIG. 1, the deposits 150 are shown in exaggerated size and shape for illustrative purposes only. Deposits 150 may be deposited on the clamping surface 114 uniformly or more generally non-uniformly. Such deposits 150 may be caused by ion beam byproducts, eg, arsenic deposition in one example. The amount of deposits 150 and the rate at which they accumulate can be weighted when driving hot implant processes, as some deposits are further drawn to the hot clamping surface. In addition, thermally activated reactions can occur on the hot clamping surface to produce additional deposits. Trace amounts of materials such as carbon, fluorine, tungsten, and hydrogen may be present in ion implanter 100. Such materials may contribute to thermally activated reactions to create additional unwanted deposits on the clamping surface 114 of the platen 112.

Preferably, the clamping power supply 172 through the circuit portion 171 is configured to provide the controller 120 with a sensed signal indicative of an AC signal provided to the pair of electrodes 160, 162. The controller 120 is configured to receive the sensed signal from the clamping power supply 172 and determine whether the sensed signal indicates deposits on the clamping surface 114 that exceed a predetermined threshold.

Referring to FIG. 2A, an enlarged partial cross-sectional view of the clamping surface 214 of the platen 212 conforming to the platen 112 of FIG. 1 with a clean clamping surface free of perceptible deposits Is illustrated. This figure also shows three protrusions 202, 204, 406 or mesas that may have a height of about 5 to 7 micrometers. Other clamping surfaces without these protrusions may have a roughened texture. FIG. 2B is a clean clamping surface, but FIG. 2A, which now has the wafer 210 in the clamped position and thus the lower surface of the clamped wafer 210 lies on the top surfaces of the protrusions 202, 204, 206. Illustrates the same enlarged partial cross-sectional view of. Finally, FIG. 2C illustrates the same enlarged partial cross-sectional view of FIG. 2A with the dirty clamping surface 214 without the wafer. In this example, deposits formed a deposited layer 216 on the clamping surface 214.

During the waferless and clean clamping surface conditions of FIG. 2A, the AC signal provided by the clamping power supply 172 to the electrodes 160, 162 may have a nominal peak to peak amplitude. have. During the wafer clamp conditions of FIG. 2B, the AC signal may have a peak-to-peak amplitude of about 6-7 times the nominal peak-to-peak amplitude of FIG. 2A. Finally, during the waferless and dirty clamping surface conditions of FIG. 2C, the AC signal may have a peak-to-peak amplitude that is greater than the nominal value of FIG. 2A but less than the value of FIG. 2B with the wafer. In one example, the amplitude of the current may be approximately 2.0 milliamps (mA) in FIG. 2A, approximately 13 mA in FIG. 2B, and approximately 8 before wafer drops and breakage have occurred in FIG. 2C. mA may be reached.

Deposits or deposited layer 216 including conductive and semiconducting deposits effectively behave as a kind of clamped semiconductor wafer that is physically closer to electrodes 160, 162 than the bottom surface of the actual clamped wafer 210. do. Depositions 216 effectively form a quasi-layer or plate that changes the capacitance of the platen 214. The peak-to-peak current amplitude in the absence of a wafer thus tends to increase in proportion to the accumulation of deposits 216. Using a three phase system (three electrode pairs or six total electrodes), each phase can be supplied with an AC signal with a phase difference of 120 ° relative to each other. If the deposits accumulate uniformly on the clamping surface 214, wafer off currents increase equally in all three phases. If deposits accumulate non-uniformly (as is likely to happen more), the waferless currents in each phase will deviate from each other, providing an indication of non-uniform deposits and excessive deposit accumulation.

Referring to FIG. 3, a plot of the peak-to-peak current (mA) of an AC signal provided to the time-clamping power supply 172 is plotted on a plurality of wafer-free time intervals that occur between wafer clamping time intervals. Illustrated over. There is no wafer between time t0 and time t1, and the clamping surface 214 of the platen 212 is clean as illustrated in FIG. 2A. The amplitude of the AC signal may have a nominal value of about 2 mA or I1. Between time t1 and time t2 the first wafer is clamped to the clamping surface and the amplitude of the AC signal can rise to a value of about 13 mA or I3. It can be observed that there is no wafer again between time t2 and time t3, and a very slight rise in the current amplitude without wafers is slightly larger than I1. This process continues at time t6 until the current level of the waferless AC signal last exceeds the predetermined amplitude threshold I2.

Once exceeded during a wafer-free time period such as time t6, the controller 120 determines that the sensed signal from the clamping power supply 172 represents deposits on the clamping surface that exceed a predetermined deposit threshold. The predetermined amplitude threshold 12 can be selected. The predetermined amplitude threshold 12 may be selected to be 2.5 mA in one embodiment. In response, the controller 120 can take corrective action. The corrective action may include initiating a sputter clean process of the clamping surface as described in more detail herein with respect to FIG. 4. The corrective action may also include stopping the operation automatically by preventing another wafer from being clamped to the platen 112. The controller 120 may control the robot 132 to prevent the robot from placing another wafer on the platen until the clamping surface is sufficiently cleaned. In this way, the possibility of wafer drop and wafer scrap can be greatly minimized. Alternatively, controller 120 may issue an alert and give the operator of the ion implanter discretion when initiating the cleaning process.

The controller 120 can also compare the rate of increase of the amplitude of the current level of the AC signal over a predetermined rate threshold over a time interval. In other words, although the predetermined amplitude threshold I2 is not exceeded by the waferless current level, it is desirable to cause the controller 120 to take corrective action if the rate of increase of the current level exceeds the predetermined rate sufficiently large. It is possible.

4 illustrates a sputter clean process that may be initiated by the controller 120 in response to the sensed signal indicating that deposits on the clamping surface exceed a predetermined deposit threshold. The controller 120 can instruct the tilt mechanism 118 to tilt the platen 112 to achieve the desired angle of incidence θ relative to the path of the particular low energy ion beam 104.

To help explain the angle of incidence θ, a Cartesian coordinate system can be defined in which the path of the ion beam 104 defines the Z axis. The Z axis crosses the orthogonal plane. The X axis is the horizontal axis in this plane. The Y axis is orthogonal to the X axis and is the vertical axis in this plane. As illustrated in FIG. 4, the platen 112 is tilted by the tilting mechanism 118 about the X axis as sometimes referred to in the art as “X-Tilt”. As illustrated in FIG. 4, the angle of incidence θ may be defined as the angle between the Y axis and the plane 404 defined by the clamping surface 114 of the platen 112.

The angle of incidence θ may be within a range of less than 90 degrees but greater than 40 degrees to increase the sputter yield. In one embodiment, the incident angle θ may be 70 degrees. A scanning system (not shown) for the platen 112 may translate the platen vertically in the Y direction during the sputter clean process such that the ion beam 104 impinges on the entire clamping surface of the platen 112. . In one embodiment, ion implanter 100 may provide a low energy (about 5 keV) Ar + ion beam having about 5 to 15 milliampere (mA) ion beam current.

The controller 120 can also monitor the removal rate of deposits during the sputter clean process by analyzing the sensed signal indicative of the amplitude of the wafer-free current level. In this way, the effectiveness of different ion beam recipes can be compared and contrasted. In addition, once the removal rate is known, the controller 120 can perform calculations to confirm the expected total cleaning time. In this way, the impact on ion implanter productivity can be minimized.

Thus, an ion implanter having a controller configured to monitor the condition of the clamping surface of the platen by monitoring the amplitude of the AC signal provided to the electrodes of the platen without a wafer clamped to the platen has been provided. Increasing the amplitude of the waferless AC signal indicates accumulation of deposits. As a result, the platen's clamping performances can be compromised if deposit buildup becomes excessive. The controller may compare the amplitude of the waferless AC signal with a predetermined amplitude threshold selected to minimize the chance of clamping failure. This allows the condition of the clamping surface to be monitored in situ during ion implantation without impacting the throughput of the ion implanter. In addition, this provides predictive capabilities for determining when a corrective action needs to be made to also ensure that cleaning is performed when needed to minimize wafer drop and break events while minimizing the number of cleaning interruptions. Corrective actions may include automatically initiating a sputter clean process and stopping ion processing of additional wafers until appropriately cleaned. This is particularly helpful for hot implants where deposit buildup is more likely to occur than room temperature implants.

The present invention is not to be limited in scope by the specific embodiments described herein. Rather, various other embodiments and modifications of the invention in addition to the embodiments described herein will become apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of the present invention. In addition, while the present invention has been described herein in the context of particular embodiments in a particular environment for a particular purpose, those skilled in the art are not limited thereto, and the present invention is not limited to any number of purposes for any number of purposes. It will be appreciated that it may be beneficially implemented in environments.

Claims (17)

As an ion implanter,
A platen having a clamping surface configured to support a wafer for processing with ions, the platen also having at least a pair of electrodes below the clamping surface;
A clamping power supply configured to provide an AC signal to the at least one pair of electrodes and provide a sensed signal representative of the AC signal; And
A controller configured to receive the sensed signal from the clamping power supply when there is no clamped wafer on the clamping surface, wherein the controller monitors the sensed signal and sets the sensed signal to a predetermined deposit threshold. The controller further configured to determine whether excess deposits on the clamping surface are indicative,
The controller determines whether the sensed signal exceeds the predetermined deposit threshold by analyzing whether the amplitude of the current level of the AC signal exceeds a predetermined amplitude threshold when there is no wafer clamped to the clamping surface. Further determine whether to indicate deposits on the phase,
The controller is further configured to initiate a sputter clean process of the clamping surface of the platen when the amplitude of the AC signal is greater than the predetermined amplitude threshold,
The controller is further configured to monitor the sensed signal during the sputter clean process and correlate the sensed signal to a removal rate of the deposits.
delete The method according to claim 1,
And the predetermined amplitude threshold is 2.5 mA at peak to peak.
The method according to claim 1,
The controller is further configured to initiate a sputter clean process of the clamping surface of the platen when the amplitude of the AC signal exceeds the predetermined amplitude threshold.
The method according to claim 1,
The controller is further configured to prevent another wafer from being clamped to the clamping surface until the amplitude of the AC signal is below the predetermined amplitude threshold.
The method according to claim 1,
And the AC signal comprises a square wave signal.
As an operation method of the ion implanter,
Providing an AC signal to at least a pair of electrodes of the platen having a clamping surface;
Monitoring the sensed signal representative of the AC signal when there is no clamped wafer on the clamping surface;
Determining whether the sensed signal indicates deposits on the clamping surface that exceed a predetermined deposit threshold when there is no clamped wafer on the clamping surface;
Determine the amplitude of the current level of the AC signal when there is no wafer clamped to the clamping surface to determine whether the sensed signal represents deposits on the clamping surface that exceeds the predetermined deposit threshold; Comparing;
Initiating a sputter clean process of the clamping surface of the platen when the amplitude of the AC signal is greater than the predetermined amplitude threshold; And
Monitoring the sensed signal during the sputter clean process and correlating the sensed signal to a removal rate of the deposits.
delete The method according to claim 7,
If the amplitude of the AC signal is greater than the predetermined amplitude threshold, the sensed signal indicates deposits on the clamping surface that exceeds the predetermined deposit threshold.
The method according to claim 7,
If the amplitude of the AC signal is less than the predetermined amplitude threshold, the sensed signal indicates deposits on the clamping surface that exceeds the predetermined deposit threshold.
The method according to claim 7,
And the predetermined amplitude threshold is 2.5 mA peak to peak.
delete delete The method according to claim 7,
Calculating an expected clean time interval in response to the removal rate.
The method according to claim 7,
Preventing the wafer from being clamped to the clamping surface until the amplitude of the AC signal is less than the predetermined amplitude threshold.
The method according to claim 1,
The controller is further configured to calculate an expected clean time interval in response to the removal rate.
As an ion implanter,
A platen having a clamping surface configured to support a wafer for processing with ions, the platen also having at least a pair of electrodes below the clamping surface;
A clamping power supply configured to provide an AC signal to the at least one pair of electrodes and provide a sensed signal representative of the AC signal; And
A controller configured to receive the sensed signal from the clamping power supply when there is no clamped wafer on the clamping surface, wherein the controller monitors the sensed signal and sets the sensed signal to a predetermined deposit threshold. The controller further configured to determine whether excess deposits on the clamping surface are indicative,
The controller determines whether the sensed signal exceeds the predetermined deposit threshold by analyzing whether the rate of increase in amplitude of the current level of the amplitude of the AC signal over a time interval exceeds a predetermined rate threshold. And further determine whether to indicate deposits on the phase.

Images